Ink jet printers are commonly used as hard copy output devices for computers. Such printers form an image by using a plurality of nozzles to form a stream of droplets of an ink and to direct those droplets on to a sheet of an ink receiving medium (typically a surface-treated paper), thus forming the image. The image may be a monochrome image, formed using a single, normally black, ink, or a full color image, formed using at least three inks of differing colors sprayed from a set of three separate nozzles. Some contemporary ink jet printers are capable of producing color images of photographic or near-photographic quality, and are often used by graphic artists to obtain rapid color proofs of illustrations which closely simulate the color illustration which will eventually be produced on a conventional printing press. Ink jet printers can also make use of more than four inks (for example, eight color CCMMYYKK printers are produced commercially) by providing the appropriate number of sets of nozzles, and permit relatively easy use of custom-blended inks when such custom inks are required for particular jobs.
Although so-called “solid ink jet” printers are known using “inks” which are solid at room temperature and which are melted before being sprayed in the liquid state, most ink jet printers are of the so-called “liquid ink jet” type and use inks which are liquid at room temperature. Such inks typically comprise a dye dissolved, or dispersed, in a solvent or suspension medium. The solvent or medium may be organic, but organic solvents are generally not favored because of environmental and toxicity problems, and hence most solvents or suspension media are aqueous, although they may contain an alcohol or a glycol as a co-solvent. Liquid inks may also contain other additives, such as stabilizers, viscosity modifiers, surfactants, bactericides, fungicides etc.
The dyes used in such liquid inks must satisfy numerous requirements. In order to produce images with the wide range of colors and highly saturated colors demanded by graphic artists, the dyes should have high extinction coefficients and good color. The dyes need to be highly soluble (or dispersible) in the solvent or carrier medium used, since an insufficiently soluble dye requires spraying an excessive amount of solvent with the dye, thus leading to undesirably slow drying of the image on the receiving sheet. The dye solution must be stable over the wide ranges of temperature and humidity likely to be encountered during distribution and storage of the ink, since even modest precipitation of solid dye crystals from the solution/dispersion will be disastrous because the narrow nozzles are readily clogged by such crystals. Finally, the color of the dyes, and thus of the image, must be essentially unaffected by (a) chemical reactions between the dye and any one of the variety of receiving sheets on which the image may be formed; (b) chemical reactions between the dye and any other dyes used to form the same image (in color ink jet printing, drops of the various colored inks inevitably come into contact on the receiving sheet, especially in areas of high color density); (c) air oxidation of the final image; and (d) photochemical reactions when the image is exposed to radiation. For obvious reasons, a graphic artist does not want a proof prepared for a client to undergo noticeable fading or color shifts simply because the client leaves the proof exposed on a desktop under office fluorescent lighting, or takes the proof outdoors for a short time in order to view it in daylight.
All these requirements tend to produce dyes which are a compromise, excellence in one property being sacrificed for acceptable behavior in another. In particular, many commercial ink jet dyes have less photostability than is desirable, and are subject to significant fading when exposed to office fluorescent lighting for lengthy periods.
Various pyrazolone dyes are known in the art. Patel et al., in Pyrazolone Dyes and Their Complexes For Use On Synthetic Fibers, J. Institute of Chemistry (India), (1999) teach certain metal complexed pyrazolone dyes for use in dyeing textiles.
As the state of the art advances and efforts are made to provide new ink jet recording systems which can meet new performance requirements and to reduce or eliminate some of the aforementioned undesirable characteristics of the known systems it would be advantageous to have new dyes which are useful in ink jet ink compositions and new ink jet ink compositions which can provide images which exhibit enhanced stability to light and ozone.